Pressure relief valves are well known in the art to control the pressure level of a fluid in a fluid system. Relief valves are normally designed to open at some predetermined level and bypass a part of or all of the fluid flow from the pump to the reservoir or to some other low pressure system. Likewise relief valves have been used to control the pressure level of pilot fluid in pilot control lines in order to control the maximum pressure level within the respective pilot control lines. U.S. Pat. No. 5,813,226 which issued Sep. 29, 1998 and assigned to the assignee hereof teaches the use of a control scheme for controlling the maximum pressure level within a fluid system without the use of separate pressure relief valves. In this pressure control scheme, a control valve is used to relieve the pressure within a conduit to control the maximum pressure level. In this control scheme, it is necessary to monitor the level of pressure within the system or conduit and when the pressure level of the fluid is predicted to reach its maximum level an electronic controller directs an electrical signal to the control valve moving it towards an open position in order to control the level of pressure therein. In order to control the pressure level within a conduit or system in which the rate of pressure rise is very rapid, the control scheme of the above noted patent functions to anticipate an increase in pressure rising beyond the predetermined maximum level and initiates movement of the control valve towards an open position prior to the maximum pressure level being reached so that the control valve would be at or very near open once the pressure raises to the maximum level. This permits the control valve to open in time to minimize any "pressure overshoot" or sometimes referred to as "pressure spike". "Pressure overshoot" is any pressure of the fluid that exceeds the preset maximum pressure level. If the rate of pressure rise is to rapid, it cannot be anticipated quick enough and the system will still be subjected to "pressure overshoot". Another potential limitation with the control scheme of the above noted patent, is that when the system is shut down and the electronic controller is turned off, the fluid within any of the conduits between the control valve and the actuator is trapped and any thermal expansion could cause damage or failure of the conduits.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.